Massive Icebergs May Affect Antarctic Sea Life and Food Chain

NASA-funded research using satellite data has shown large icebergs that have broken off from Antarctica's Ross Ice Shelf are dramatically affecting the growth of minute plant life in the ocean around the region -- plant life vital to the local food chain.

Scientists say the icebergs appear to have caused a 40 percent reduction in the size of the 2000-2001 plankton bloom in one of Antarctica's most biologically productive areas. The icebergs decrease the amount of open water that the plants need for reproduction.

After the calving, or "breaking off," of the B-15 iceberg in March of 2000, researchers used imagery from NASA's SeaWiFS (Sea-viewing Wide Field-of-view Sensor) satellite and data from the Defense Meteorological Satellite Program to see the effect that large icebergs have on phytoplankton (minute floating plants) blooms. The B-15 iceberg that broke off the Ross Ice Shelf and drifted into the southwestern Ross Sea was as large as the state of Connecticut (approximately 10,000 square kilometers or 3,900 square miles).

Thorsten Markus of Goddard, a co-author on the paper, noted that SeaWiFS satellite imagery enabled researchers to see that large icebergs such as the B-15 restricted the normal drift of pack ice. Normally, when the winds shift, ice is carried out into the Ross Sea, creating open ocean space and a breeding ground for phytoplankton. The icebergs, however, created a blockage that resulted in heavier spring/summer pack-ice cover than previously recorded.

Since the area of sea ice was more extensive, the area suitable for phytoplankton growth was reduced, and as a result, so was the length of the algal growing season. Since the B-15 iceberg was so large, plankton productivity throughout the region was more than 40 percent below normal.

For the complete article on the Antarctica icebergs and its affects on plant life, go to: http://www.gsfc.nasa.gov/topstory/20020416iceberg.html